Dairy products discharged into the sewer of a dairy plant generally represent from one to three percent of the total production, and even more, depending on the activities. These losses constitute an environmental contaminant which must nowadays be eliminated at high costs in a biological process, most often of the aerobic type. Elimination of the muds constitutes an important constraint in an aerobic biological process. In view of decreasing these costs, an attempt to subject the sullage proteins to a methane-generating pretreatment has been made. This process is not basically enticing, since proteins are substances which are too valuable to be downgraded to combustible state. Moreover, although it does decrease the cost of waste treatment, the methane-generating process has high fixed costs, which brings its total operating cost way above a redeemable threshold.
Conventional physico-chemical treatment of sullage is inadequate in the dairy industry, if one wishes to recycle the milky products as foodstuff, because of the nature of the chemical products involved. Amongst these products, aluminum and iron salts are normally found. Aluminum must be excluded because of the its toxicity to Man. Iron cannot be used in the dairy industry, because it has a destructive catalytic effect over the basic elements of milk. Furthermore, iron salts are not recommended for animal feeding, since they color the meat, thus decreasing its commercial value.
The cost of eliminating the metals contained in the muds generated by the conventional physico-chemical treatment is again prohibitive, and somehow or other, it cannot be completed but for concurrent downgrading of the associated organic compounds. The products that usually result from this treatment, due to their high relative mineral yield, do increase the ash content of the treated products, and this is not appreciated in the dairy business when this mineral yield does not entail a financial return. Reduction to powder of the treated product by spraying is impossible, since the metallic precipitates give to the treated product a heterogeneous granular structure which chokes the equipment and, more particularly, the spraying nozzles. Roll drying remains possible but the operating costs are high and clogging has to be closely controlled. The end product does not appear in the shape of a homogeneous powder, but in the form of particles or flakes, which are highly colored when iron salts have been used for the treatment. Because of its heterogeneity and of its lack of fluidity, further handling of the product, such as putting it into bags, is problematic. Under their own weight, the flakes cling with one each another to form a clod, and this may affect the whole production.
Utilization of metal-based reagents would not be the sole barrier for applying the conventional physico-chemical processes to the dairy industry. A further contraindication of conventional processes is that they entail the use of synthetic adjuvants, which are indispensable to prevent work-heavy treatment.
Indeed, should they be used for the dairy industry sullage treatment, these synthetic chemical products would be integrally found in the final milk products. Now, innocuousness of ingested synthetic organic adjuvants is not established, and it would be abusive to have them brought into our alimentary chains. It may be said that a few countries allow the use in the treatment of their drinking water of some synthetic adjuvants, although it must be understood that the adjuvants are not any more suitable to be present in treated water than the jointly-injected metal-based salts.
In conclusion, conventional physico-chemical processes cannot be applied in the profitable recycling of the dairy industry sullage, in view of the non-alimentary nature of the reagents used and of the fact that it is impossible to evaporate and dry out the recuperated dairy products.